The present invention relates generally to an aqueous adhesive composition for bonding reinforcing textile yarns and fabrics to rubber products, which contains an epoxy resin having an epoxy functionality of three or greater.
Textiles are used extensively to reinforce rubber products such as tires, v-belts, and conveyor belts. The textile may be in the form of a fiber, yarn, or a woven, knitted or non-woven fabric. Fibers typically used for reinforcement are manufactured from polyamides, including nylons and aramids, polyesters, particularly polyethylene terephthalate, rayon and glass fibers.
One of the difficulties encountered in manufacturing reinforced rubber products is that the textile fibers do not adhere well to the rubber without additional chemical treatment. A number of systems have been developed to promote adhesion of the fiber to the rubber. One such system is based on pretreatment of the textile fibers with an adhesive to promote bonding. The textile is dipped in the adhesive composition, which is usually an aqueous latex, followed by drying and curing.
The most common pretreatment system is based on an adhesive containing resorcinol-formaldehyde latex (RFL), usually in combination with a functionalized butadiene or styrene butadiene latex. Examples of functionalized latices include copolymers of conjugated dienes with vinylpyridine, unsaturated carboxylic acids, and cyanated vinyl monomers. Representative adhesive compositions may be found in the following United States patents:
Girgis, U.S. Pat. No. 4,405,746; PA1 Toyoda et al., U.S. Pat. No. 4,963,613; PA1 Sekigushi et al., U.S. Pat. No. 5,236,742; and PA1 Hisaki et al., U.S. Pat. No. 4,286,783.
Some textile fibers, especially aramid and polyester fibers, require a two-step treatment to ensure good adhesion of the textile and rubber product. For example, the textile product may be first treated with a polyisocyanate, polyepoxide, polyamine, or ethylene urea followed by treatment with the RFL-functionalized diene latex formula. Of course, the two-step or double-dip treatment increases the process steps and is undesirable from an economic point of view.
Another system used to promote the adhesion of reinforcing textiles to rubber products is to incorporate additives into the rubber itself. Thus, in Durairaj, U.S. Pat. No. 5,030,692 a resorcinol-formaldehyde resin is compounded in the rubber to improve the mechanical properties of the rubber and promote tire cord to rubber adhesion.
One of the drawbacks of systems incorporating resorcinol-formaldehyde resins, whether used to pretreat the textile or for incorporation into the rubber itself, is the relative toxicity of resorcinol and formaldehyde and their undesirability in the workplace. Another shortcoming of the use of resorcinol-formaldehyde latex pretreatments is that the RFL adhesives must be aged before use and have a limited shelf life.
In Singh et al., U.S. Pat. No. 5,298,539, a vulcanizable rubber composition is provided having a derivative of melamine, acetoguanamine, etc. incorporated therein. The rubber composition has improved toughness and adhesion to tire cord. Nevertheless, it is desirable to provide an adhesive composition which does not require compounding additives into the rubber product itself.
All of the aforementioned patents are incorporated by reference herein.